Cooled brush holder for carrying current in dynamo-electric machines



Se t. 14, 1965 B. BERGER ETAL COOLED BRUSH HOLDER FOR CARRYING CURRENTIN DYNAMO-ELECTRIC MACHINES 6 Sheets-Sheet 1 Filed May 29, 1961 Se t.14, 1965 B. BERGER ETAL 3,206,630

COOLED BRUSH HOLDER FOR CARRYING CURRENT IN DYNAMO-ELEGTRIC MACHINES 6Sheets-Sheet 2 Filed May 29. 1961 Sept. 14, 1965 B. BERGER ETAL3,206,630

COOLED BRUSH HOLDER FOR CARRYING CURRENT IN DYNAMO-ELEGTRIC MACHINES 6Sheets-Sheet 3 Filed May 2-9. 1961 Til 17 mm Q nnnnn/ Sept. 14, 1965 B.BERGER ETAL 3,206,630

COOLED BRUSH HOLDER FOR CARRYING CURRENT IN DYNAMO-ELECTRIC MACHINESFiled May 29. 1961 6 Sheets-Sheet 4 p 1965 .BERGER ETAL 3,206,630

COOLED BR HOLDER FOR CARRYING CURRENT IN DYNAMO-ELECTRIC MACHINES FiledMay 29, 1961 s Sheets-Sheet s Filed May 29, 1961 Sept. 14, 1965 B.BERGER ETAL 3,206,630

COOLED BRUSH HOLDER FOR CARRYING CURRENT IN DYNAMIC-ELECTRIC MACHINES 6Sheets-Sheet 6 3,206,630 Patented Sept. 14, 1965 ICE 3,206,630 COOLEDBRUSH HOLDER FOR CARRYING CUR- RENT IN DYNAMO-ELECTRIC MACHINES BrunoBerger and Norman E. Gatiss, Newcastle-upon- Tyne, England, assignors toC. A. Parsons & Company Limited, Newcastle-upon-Tyne, England Filed May29, 1961, Ser. No. 113,523 Claims priority, application Great Britain,May 31, 1960, 19,189/ 60 8 Claims. (Cl. 310227) This invention relatesto brush gear for carrying current in dynamo-electric machinesespecially slip ring brush gear of the kind commonly used with largeturbo-generators for power station use.

As the current rating of such machines increases complications arise asa result of the large number of brushes required to carry the rotorcurrent. If the diameter of the slip ring is increased to accommodatethe extra brushes the rate of wear is increased and current sharingdifiiculties are enhanced because of resulting higher rubbing speeds. Onthe other hand if the rows or number of brushes is increased the lengthof the machine is increased or routine inspection and maintenance iscomplicated. If the current is increased without raising the number ofbrushes, resulting brush temperature rises would not be permissible.

The object of the present invention is to provide improved brush gearfor current carrying in dynamo-electric machines in which the abovecomplications are substantially reduced.

The invention consists in brush gear for current carrying indynamo-electric machines in which the brush gear is liquid cooled asspecifically defined in the appended claims.

Referring to the accompanying drawings.

FIGURE 1 shows an exploded perspective view of a brush box of brush gearin accordance with one form of the present invention;

FIGURE 2 is a plan view of the brush box of FIG- URE 1.

FIGURE 3 is a section on line XX of FIGURE 2.

FIGURE 4 shows a perspective view of part of a brush gear assembly inaccordance with one form of the invention.

FIGURE 5 is a front elevation of a brush box and bracket for use withvaporised liquid cooling.

FIGURE 6 is a plan view of FIGURE 5.

FIGURE 7 is an end elevation of FIGURE 5.

FIGURE 8 is a section on line AA of FIGURE 7.

FIGURE 9 is a section on line BB of FIGURE 7.

FIGURE 10 is a section on line CC of FIGURE 7.

FIGURE 11 shows a brush box and bracket of the kind illustrated inFIGURE 4 adapted for thermo-electric cooling of the brush flexible lead.

FIGURE 12 shows a section through a brush and associated brush box in anarrangement which dispenses with the need for flexible leads for thebrushes.

In carrying the invention into effect in the forms illustrated by way ofexample and referring first to FIGURE 1, a brush box 1 is formed withopenings 2 in which brushes are housed. A channel 3 surrounds theopenings 2 and a cooling liquid such as water is circulated, for exampleby means of a pump, through the channel 3 to cool four sides of thebrushes. Inlet and outlet connections for the cooling liquid are shownat 4 and 5 respectively.

A cover plate 6'fits over the box and is welded or otherwise joinedthereto.

The brush box may be cast in a material such as aluminium and whilst twoopenings for brushes have been shown the invention is not limited tothis number.

Referring to FIGURES 2 and 3 the shape of the channel 3 can be moreclearly seen.

Cooling liquid entering through inlet 4 is deflected by a wall 7 toensure that the liquid circulates around the brushes and not directlyfrom the inlet 4 to the outlet 5. If necessary the inner surface of thebox 1 in contact with the cooling liquid may be finned to improve heattransfer.

An assembly of a number of such boxes on a dynamoelectric machine isshown in FIGURE 4, the boxes being connected in parallel with supply anddischarge pipes 8 and 9 respectively for the cooling liquid.

Each brush box is attached to a bracket 10 by means of bolts 11 (seeFIGURE 1) and the brackets are in turn fixed to a brush gear supportplate 12 on the machine. Brushes 13 are shown in position in two of theboxes and are connected to terminals 14 by current carrying flexibleleads 15 in conventional manner. These flexible leads must be rated atthe brush operating current and this will require any increased coppersection and generally four flexible leads instead of the two normallyused.

With the arrangement described the current density for each brush can beincreased four of five times without damage or increase in temperatureor undue increase in,

the rate of wear of the brushes.

Whilst in the form described .the boxes are forcedcooled by a liquidwhich is circulated, for example by means of a pump, through each boxfrom common inlet pipes 8, a vaporisable liquid can be used within thescope of the invention. In such a case each brush box would beindividually sealed and natural circulation of the liquid and vapourwould take place within the box; for example a brush box and bracketcould be a single hollow casting with the liquid forming a reservoiraround the brushes and the vapour rising into the space in the bracketabove the brushes, condensing and running back into the reservoir ofliquid surrounding the brushes. This arrangement would necessitate allthe brush boxes being above the centre line of the machine so that therequired circulation could take place.

FIGURES 510 show a sealed brush box suitable for use with vaporisationcooling. The brush box 16 and bracket 17 are hollow and the cavities orchannels 18 surrounding the brushes 19 open into the cavity 20 of thebracket.

The cavities 18, 20 are filled with a vaporisable liquid, such as Freon,to a level, in the bracket cavity 20, which is above the brushes. Theremainder of the space in the cavity 20 above the liquid is the spaceinto which the vapour rises and is condensed to flow, under gravity,back into the liquid. An inspection window 21 is provided to check theliquid level.

To produce condensation in the upper part of cavity 20 the brush box andbracket are cooled by a gas circulating over the outside surfacesthereof. Fins 22 may be provided, as shown, to assist transfer of heatto the cooling gas. The use of a gas, such as nitrogen, hydrogen orargon or other gas without free oxygen content, reduces oxidation of thebrushes and hence increases brush life.

The use of a gas such as nitrogen, hydrogen or argon as coolant meansthat the brush gear covers cannot be removed for spring pressureadjustments or brush changes unless the gas is first removed or unlessit is allowed to escape to atmosphere. It is preferable, therefore, toeliminate as far as possible the need for access to the brush gearduring the running period of the machine between routine overhauls orshut-down periods. To these ends long brushes up to at least 6" andconventional constant tension springs 23 which apply a pressure which isindependent of the brush length, may be used.

Instead of using sealed brush boxes as described in FIGURES -10 withcondensation taking place within the box, the vaporised liquid can betaken to a condenser separate and if desired some distance from thebrush gear. This separate condenser can then be used for condensingvapour from all the brush boxes. The condensate may return to the boxesby gravity or be circulated by means of a pump.

If a separate condenser is used the heat passing to the cooling gas issubstantially reduced and such heat can be disispated by the brush gearenclosure, assisted by the circulation produced by the rotating sliprings. If a separate condenser is not used and the system of FIGURES5-10 is used, it may be necessary to force-circulate the gas round acircuit including a cooler for the gas.

Whilst the use of a cooling gas has been described with particularreference to its use when vaporisable liquids are used for cooling thebrushes, such a gas could also be used to surround the brush gear ofFIGURES 1-4.

Instead of having hollow boxes the brushes may be cooled by brazingcooling pipes to solid brush boxes and connecting the pipes to the pipes8 and 9 of FIGURE 1, for example, to permit ingress and egress ofcoolant. The tubes may be flattened tubes to give a good surface area ofcontact with the brush box.

As a consequence of the increased current capacity of the brushes due toimproved brush cooling devices as described above, the number of brushesrequired for a machine can be reduced. This in turn means that as eachbrush is carrying a greater proportion of the total current it isimportant to know when a brush is being overloaded. To keep a check onthe current being carried by any given brush, a resistance 24 may beincorporated in the current path between the brush flexible leads 25 andthe bracket 17 as shown in FIGURES 5 and 7. Leads can be taken fromterminals 24a, 24b at each end of the resistance and taken to a selectorswitch which in turn is connected to a voltmeter for recording thevoltage drop across any given resistance to determine the currentpassing therethrough. The current carried by each brush can therefore bedetermined and if one or more brushes are seriously overloaded remedialaction can be taken before damage to any part of the brush gear occurs.An alarm contact can be incorporated in the voltmeter and the selectorswitch can be motorised, for remote indication of overload for examplein a control room. To keep the heat generated in the brush flexibleleads small, with increased current flowing in the leads, thecross-sectional area of the lead is increased. A limit is reached,however, when the lead presents appreciable restraint to the freemovement of the brush and it may be necessary to increase and direct theflow of cooling gas or use other cooling means. For example, theflexible lead may be cooled by making use of the well knownthermoelectric cooling eflect of P and N- type thermoelements interposedin the electrical circuit at each end of the brush flexible lead.

FIGURE 11 shows how such a cooling device can be applied to a brush boxand bracket of the type shown in FIGURE 4. Because of the improvedcooling only one flexible lead is normally required. Assuming that thecurrent is flowing from the brush 13 to the bracket 10, a P-typethermo-element 26 is joined to a copper heat sink 27 at the end of theflexible lead remote from the brush 13. The N-type thermo-elemcnt 28 isjoined to a copper heat sink 29. The heat sink 27 plugs into or isotherwise fastened to the bracket 10 and the heat sink 29 is pluggedinto or otherwise fastened to copper extension 30 of the brush 13. Theflexible lead With its thermo-elements and heat sinks thus forms adetachable connection, which allows the brush to be renewed withoutrenewing the flexible lead. Some of the heat developed in the flexiblelead 15 is absorbed at the junctions of the thermo-elements 26 and 28and the flexible lead 15. Additional heat due to the Peltier effect isgenerated at the junction of the thermo-elements 26 and 28 and the heatsinks 27 and 29 respectively. The total heat appearing at these latterjunctions is absorbed by the cooling liquid and the bracket. Some heatwill also be dissipated to the gas surrounding the brush boxes andbrackets.

If the current flow is from bracket to brushes the positions of the Pand N-type elements would be reversed.

The need for removing heat developed in the flexible leads can beavoided by dispensing with the flexible leads altogether. Such anarrangement is illustrated in FIG- URE 12 in which a graphite orcopper-graphite sleeve 31 is interposed between a brush 32 and the wallof the brush box 33. Current then passes from the brush through thesleeve to the brush box or vice versa and the need for brush flexibleleads is avoided. The heat developed at the junction between sleeve andbrush is readily removed by the cooling fluid.

We claim:

1. Brush gear for carrying current in dynamo-electric machines whichbrush gear is vaporisable-liquid cooled, and in which the brushes arehoused in boxes attached to brackets which are in turn attached to abrush gear supporting ring, each bracket and associated brush boxesbeing hollow with connected cavities therein surrounding the brushes andin the bracket, said cavities being filled to a level above the brusheswith the va-porisable liquid, a space being formed in the bracket cavityabove the liquid level into which vapour may rise and be condensed.

2. Brush gear for carrying current in dynamo-electric machines whichbrush gear is vaporisable-liquid cooled, and in which flexible leadsconnected to the brushes and carrying current to or from the brushes arecooled by connecting to one end of the lead a thermo-element of the P-type and connecting to the other end a thermo-element of the N-type eachthermo-element being joined to a metal member acting as a heat sink fromwhich heat is dissipated to the liquid cooling the brushes and to thegas surrounding the brush gear.

3. Brush gear for carrying current in dynamo-electric machines whichbrush gear is vaporisable-liquid cooled, and in which flexible leadsconnected to the brushes and carrying current to or from the brusheseach have a resistance in series therewith the voltage drop across whichresistance is measured to provide an indication of the current flowingthrough the flexible lead.

4. Brush gear for carrying current in dynamo-electric machines whichbrush gear is vaporisable-liquid cooled, and in which inside the brushbox a sleeve of high electrical and thermal conductivity acts as thecurrent transfer contact between box and brush, thereby dispensing withflexible leads.

5. Brush gear for dynamo-electric machines comprising hollow brushboxes, brushes located in said boxes, said brush boxes having connectedcavities therein surrounding the brushes, the cavities containing avaporisable liquid and means connected with the liquid space in saidboxes for condensing vapour produced from said liquid.

6. Brush gear as claimed in claim 5 in which each brush box is selfcontained and the means connected to the liquid space for condensing thevapour comprise a space in the box above the liquid level into which thevapour may rise and be condensed by cooling fluid circulating over theboxes.

7. Brush gear as claimed in claim 5 in which the means connected to theliquid space of each box for condensing vapour is a separate condenserlocated remote from said brush gear and connected thereto by conduitsfor the passage of vapour and condensate.

8. Brush gear for dynamo-electric machines comprising hollow brush boxesfor housing brushes and means for liquid cooling the brushes in saidboxes and brush leads conveying current to or from said brushes in whichthe brush leads comprise a sleeve of high electrical and thermalconductivity interposed between a brush and its brush box, which sleeveacts to transfer current from the brush References Cited by the ExaminerUNITED STATES PATENTS Barry 310227 Burke 310227 Saathoif 310-54 Jacobsen310-227 Lanter 310-227 Turner 31054 Labastie 310-227 Else 310227 Caputoet a1. 310-227 Kocher et a1 31054 X to the box or vice-versa and iscooled by the liquid in the 15 MILTON 0 HIRSHFIELD, primary Examinersaid boxes.

5. BRUSH GEAR FOR DYNAMO-ELECTRIC MACHINES COMPRISING HOLLOW BRUSHBOXES, BRUSHES LOCATED IN SAID BOXES, SAID BRUSH BOXES HAVING CONNECTEDCAVITIES THEREIN SURROUNDING THE BRUSHES, THE CAVITIES CONTAINING AWVAPORISABLE LIQUID AND MEANS CONNECTED WITH THE LIQUID SPACE IN SAIDBOXES FOR CONDENSING VAPOUR PRODUCED FROM SAID LIQUID.